Apparatus and method for contactless transfer and soldering of chips using a flash lamp

ABSTRACT

A method and apparatus for soldering a chip (1a) to a substrate (3). A chip carrier (8) is provided between a flash lamp (5) and the substrate (3). The chip (1a) is attached to the chip carrier (8) on a side of the chip carrier (8) facing the substrate (3). A solder material (2) is disposed between the chip (1a) and the substrate (3). The flash lamp (5) generates a light pulse (6) for heating the chip (1a). The heating of the chip (1a) causes the chip (1a) to be released from the chip carrier (8) towards the substrate (3). The solder material (2) is at least partially melted by contact with the heated chip (1a) for attaching the chip (1a) to the substrate (3).

CROSS-REFERENCE TO RELATED APPLICATIONS

This patent application is a U.S. National Phase of PCT InternationalApplication No. PCT/NL2016/050296, filed Apr. 26, 2016, which claimspriority to European Application No. 15165474.6, filed Apr. 28, 2015,which are both expressly incorporated by reference in their entireties,including any references contained therein.

TECHNICAL FIELD AND BACKGROUND

The present disclosure relates to soldering, in particular to anapparatus and method for soldering chips to a substrate.

Simple flexible systems, such as logic functions with transistors oroptoelectronic devices, can in principle be fully printed on a substrate(e.g. foil or rigid board). However, for more complex systems, there isa need to develop hybrid systems in which printed circuitry is combinedwith silicon-based integrated circuits or surface mounted device (SMD)components, referred herein as chip components or simply “chips”. Tofunctionalize the device, multiple chip components, often havingdifferent dimensions, may need to be interconnected to the circuittracks on the substrate, e.g. printed or etched copper circuits. Thiscan be realized for example using oven reflow soldering, conductingadhesive bonding or face-up chip integration. However, these processesare considered time consuming and/or incompatible with low-costpolyester foils having low decomposition temperatures. Especially forsoldering process, commonly used polymer substrates tend to degrade anddeform under thermal load above 150° C.

For example, reflow soldering can typically be used for interconnectingthick chips on a rigid substrate board such as FR4 or ceramics. However,reflow soldering, is poorly compatible with low-cost flexible foils androll-to-roll (R2R) processing because it requires maintaining the wholeboard above the liquidus temperature of the solder which is generallyabove 200° C. for long holding time. This typically results in atime-consuming process using large in-line ovens, often having multipleloops. The long holding time may also cause deformation or degradationof the flexible foil itself or degradation of its organic surfacecoatings or adhesives. It is considered impossible to oven reflowconventional solder on low-cost polyester foils, such as polyethyleneterephthalate (PET), by using industry standard lead-free alloys becausePET has a maximum processing temperature of around 120° C.-150° C.,which is much lower than the liquidus temperature of these solders(>200° C.).

As an alternative, for example, infrared (IR) heating can be used withcomparable soldering time. For example, infrared laser spots can be usedto heat each solder connection sequentially. However, in laser spotsoldering, the small spot area may require precise positioning of thespot for each component. Furthermore, applying this technology in a R2Rprocess is challenging as the laser spot needs to align to multiplechips on a moving substrate. Furthermore, the process can be timeconsuming. Accordingly, some of these methods may still be based on stopand go.

As another alternative, large area illumination by a high-energy lightpulse of a flash lamp can be used. For example, an article in ElectronicMaterials Letters, Vol. 10, No. 6 (2014), pp. 1175-1183 by Van den Endeet al. describes Large area photonic flash soldering of thin chips onflex foils for flexible electronic systems. Advantageously, when thetimescale of the heating pulse is short enough to avoid diffusiveheating of the flexible polymer substrate, components can be soldered attemperatures higher than the maximum processing temperature of thefoils. However, if the absorption of light by the (foil) substrateand/or components differs, this can lead to selective heating.Furthermore, electronic devices, generally consist of multiple chipcomponents. This may lead to further differences in heating behaviourfor the different components which makes the temperature and solderprocess difficult to control.

Accordingly, there remains a need for improvement in the soldering ofchips to a substrate, e.g. faster, more reliable, compatible withflexible foil substrates, roll-to-roll processing, and different chipsand/or substrates.

SUMMARY

One aspect of the present disclosure may be embodied as a method forsoldering a chip to a substrate. The method comprises providing a chipcarrier between a flash lamp and the substrate. The chip is attached tothe chip carrier on a side of the chip carrier facing the substrate. Asolder material is disposed between the chip and the substrate. Forexample the solder material can be provided on the substrate where thechips are to be placed, at an underside of the chips, or both. A lightpulse is generated with the flash lamp for heating the chip. The heatingof the chip causes the chip to be released from the chip carrier towardsthe substrate. Furthermore, the solder material is at least partiallymelted by contact with the heated chip for attaching the chip to thesubstrate after re-solidification of the solder material.

Advantageously, the light pulse can be used for both releasing the chipsfrom the carrier substrate and heating the chips for soldering. Forexample, heating of the chips may cause the chips to be released fromthe substrate by partial decomposition of the carrier and/or asacrificial adhesive layer between the chip and carrier. Furthermore,decomposition by heating may cause rapid gas formation that can increaseimpulse of the chip thereby launching it towards the substrate. Thelight pulse from a flash lamp is found particularly advantageous in thisrespect because it can deliver a high energy light pulse with over arelatively large area with homogenous intensity and with a relativelylong pulse length e.g. on the order of milliseconds. Additionally, amasking device may be used to pattern the light from the flash lamp,e.g. to irradiate only the positions of the chips and leave the rest ofthe carrier and substrate unaffected.

Flash lamp induced transfer may be contrasted e.g. with laser inducedtransfer, wherein the chips may tend to flip in mid-air because it ismore difficult to generate a homogeneous light intensity over a largerarea. For example, when the light intensity is higher on one side of thechip, delamination can occur earlier at that particular spot. Comparede.g. to robotic arms used in pick and place equipment, the throughputcan be higher using light induced transfer of chips combined withsoldering.

When using relatively long millisecond pulses that are typical for ahigh energy flash lamp, the chips may also be continuously heated, afterrelease, while in mid air between the carrier and destination substrate.The chip can be heated relatively fast while in mid air if it is notcontacting a heat sink such as the substrate and a relatively hightemperature can be achieved. By modulating an intensity of the pulse, itcan be adapted to different phases of the transfer, e.g. with lessintensity during the transfer in mid air to prevent overheating. Lightmodulation can e.g. be effected by a masking device and/or control ofthe flash lamp. Alternatively, or in addition, by projecting the lightpulse onto the chips while they are positioned on the substrate with thesolder material there between, the chips can be heated and cause atleast partial melting of the solder material for attaching the chips tothe substrate.

The present methods can also be used for simultaneous transfer ofmultiple chips at once, in particular using a single light pulse.However, when different of chips are transferred, the chips can havedifferent heating properties, e.g. caused by different dimensions(surface area and/or thickness), heat capacity, absorptivity,conductivity, number and/or size of solder bonds, etcetera. Thedifferent heating properties can make it difficult to uniformly controlthe transfer and soldering. To alleviate this problem, a masking devicecan be disposed between the flash lamp and the chips causing differentlight intensities in different areas of the light pulse passing themasking device. The different chips can thus be heated with thedifferent light intensities from a (single) light pulse.

Using different light intensities, e.g. power or energy per unit area,may at least partially compensate the different heating properties ofthe chips to reduce a spread in temperature between the chips as aresult of the heating by the light pulse. The different chips may e.g.attain a predetermined temperature in a relatively small temperaturerange for melting the solder material in contact therewith in acontrolled manner. It will be appreciated that the present technique hasthe advantages of a flash lamp exposure, e.g. being relatively fastbeing able to expose large areas with multiple components, compatiblewith flexible foils and roll-to-roll processing due to the pulseduration and intensity. Furthermore, by use of the masking device, thetechnique can be reliable e.g. due to improved control over the heatingof different chips. The masking device can also be used to preventexposure of the substrate, e.g. at places between the chips. This mayprevent damage to the substrate.

By simultaneously transmitting a single pulse to the chips via a maskpattern of the masking device, multiple chips can be exposed atdifferent intensities. For example the mask pattern comprises filterregions that selectively attenuate different areas of the pulseimpinging the mask. Accordingly, different intensities in a range up tothe original intensity of the light pulse can be achieved. For example afirst intensity can be set between ten and ninety percent lower orhigher than a second intensity. The masking device may have a variabletransmission or reflection across its surface to attenuate or otherwiseselectively pass part of the light to the chips. For example, themasking pattern may have a variable transmission, reflection, and/orabsorption coefficient.

The masking device can be based on reflection and/or transmission andmay comprise e.g. a fixed or variable mask pattern. For example, avariable mask pattern can be achieved by electronic control of digitalmirrors, LCD, or other tuneable optics. A variable mask pattern may beformed e.g. by a grid of pixels that can switch their transmissioncoefficient depending on a control signal. A variable light intensitycan e.g. be achieved by setting multiple pixels to the same specifictransmission coefficient or by using a combination of pixels withdifferent transmission coefficients combined.

Accordingly different light intensities suitable for soldering ofdifferent chips can be attained. For example a total energy delivered tothe chip per pulse can be tuned to a heat capacity of the chip, e.g.determined by its dimensions and/or material composition. For examplewhen a chip is relatively thin, it may be heated faster than arelatively thick chip by the same energy per surface area or lightintensity. A chip that has a larger surface area may receive more lightfrom the pulse, but it may also cool down faster via a larger contactarea. To calculate the desired light intensity, a heat capacity of thechip can also be normalized with respect to its surface area receivingthe light.

The masking device and chip carrier can be separate or integrated, e.g.in a single foil with different transmission properties at differentareas where chips are attached. In addition, by using a transparent chipcarrier, the chip can be heated by the light pulse transmitted throughthe chip carrier. The masking device can be placed between the flashlamp and the chip, e.g. for at least partially blocking part of thelight pulse from directly irradiating the substrate around the chip orfor attenuating the pulse depending on the heating properties of the oneor more chips. The masking device may also be integrated as part of thechip carrier, e.g. as a pattern on a flexible foil holding the chips.

Aspects of the present disclosure may also be embodied as an apparatusfor soldering a chip to a substrate. The apparatus comprises a substratehandler configured to determine a location of the substrate. A carrierhandler is configured to determine a location of a chip carrier with thechip attached on a side of the chip carrier facing the substrate. Analignment device and controller are configured to align the chipattached to the chip carrier with respect to a destination position ofthe chip on the substrate. A flash lamp is configured to generate alight pulse for heating the chip. The apparatus can e.g. be used forperforming the methods described herein and vice versa. Accordingly, theheating of the chip may cause the chip to be released from the chipcarrier towards the substrate wherein a solder material between the chipand the substrate is at least partially melted by contact with theheated chip for attaching the chip to the substrate.

Further aspects may be embodied as an apparatus comprising a maskingdevice disposed between the flash lamp and the chips and configured tocause different light intensities in different areas of the light pulsepassing the masking device for heating the chips, having differentheating properties, with different light intensities. For example acontroller can be used to control one or more parts of the apparatus inaccordance with the methods described herein. Accordingly, the apparatuscan be controlled such that the different light intensities may at leastpartially compensate the different heating properties of the chips toreduce a spread in temperature between the chips as a result of theheating by the light pulse.

The masking device may e.g. comprise a mask pattern with differentfilter regions. For example, two, three or more filter regions withdifferent optical properties can be provided for selectively heating twoor more chips with different light intensities while at least partiallyblocking light otherwise radiating the substrate between the chips. Forexample, different filter regions may comprise different transmission,reflection and/or absorption coefficients. Light may reach the chipse.g. via transmission through the mask or by reflection from the mask.The mask pattern area can e.g. be homogenously illuminated by optionalillumination optics between the flash lamp and the mask. The apparatusmay also comprise optional projection optics to image the mask patternonto the chips. Alternatively, the mask can be placed close to thesubstrate and/or a relatively collimated beam of light is used toproject a pattern of the mask without further optics. The projectedpattern may comprise e.g. three or more different light intensities,i.e. at least two different intensities for the two different chips anda third intensity for the surrounding substrate.

A chip location device can be configured to determine locations of thechips e.g. relative to the substrate and/or masking device. For example,the chip location device may determine the location by placing the chipsin a predetermined or otherwise known location. Alternatively or inaddition, a chip sensor, e.g. camera, can be used to detect anddetermine a location of the chips. Also a size of the chips maydetermined at the same time as placement, or by sensor detection, e.g.using a camera. Accordingly, the position and intensity of the lightdetermined by the mask pattern can be controlled depending on theposition and size of the chips. A controller may synchronize a locationof the chips with intensities of the projected mask pattern. Forexample, the controller may control the transmission coefficients of themask filter regions in dependence of the respective sizes of the chips.For example, by setting a relatively lower light intensity for a part ofthe light pulse intended for a relatively smaller size chip, the chipcan be heated to the same temperature as a relatively larger chipirradiated by a relatively higher light intensity.

For example, chips can be positioned on the substrate by a chip supplyunit such as a pick and place device with the solder material therebetween before being illuminated by a light pulse. Alternatively, chipscan be placed by illumination a chip carrier foil that releases thechips over the substrate while simultaneously heating the chip forsoldering. By additionally using the masking device, chips withdifferent heating properties, e.g. different sizes, can be contactlesslytransferred from the carrier to the destination substrate. The maskingdevice and the chip carrier can be separate devices or integrated as asingle piece, e.g. comprised in a flexible foil. The chip carrier and/ormasking device can be moves in synchronicity with the substrate to placethe chips at the intended locations while keeping the substrate movinge.g. in a roll-to-roll process. Alternatively, or in addition, thesubstrate handler may slow down or stop movement of the substrate whilethe light is applied to the chips.

The apparatus may comprise a solder supply unit to apply the soldermaterial to the substrate and/or chips before the chips are placed onthe substrate with the solder material there between. For example, ablade coating device and/or a stencilling device can be used to applythe solder material, e.g. solder bumps to conductive tracks on thesubstrate where the chip is to be placed. The apparatus may comprise a atrack application unit, e.g. printing device to apply conductive tracksto the substrate before the solder material is applied. Alternatively,or in addition the substrate may also be supplied with tracks alreadyformed.

BRIEF DESCRIPTION OF DRAWINGS

These and other features, aspects, and advantages of the apparatus,systems and methods of the present disclosure will become betterunderstood from the following description, appended claims, andaccompanying drawing wherein:

FIGS. 1A and 1B schematically show steps for soldering a chip onto asubstrate;

FIGS. 2A and 2B schematically show a further embodiment comprising mask;

FIGS. 3A and 3B schematically show a embodiments wherein a chip carrierand mask are integrated;

FIGS. 4A and 4B show steps for soldering multiple different chips atonce;

FIGS. 5A and 5B schematically show heating a chip with a tuneable mask;

FIGS. 6A and 6B schematically show embodiments for stages of solderingchips onto a substrate using a roll-to-roll process.

DESCRIPTION OF EMBODIMENTS

In some instances, detailed descriptions of well-known devices andmethods may be omitted so as not to obscure the description of thepresent systems and methods. Terminology used for describing particularembodiments is not intended to be limiting of the invention. As usedherein, the singular forms “a”, “an” and “the” are intended to includethe plural forms as well, unless the context clearly indicatesotherwise. The term “and/or” includes any and all combinations of one ormore of the associated listed items. It will be understood that theterms “comprises” and/or “comprising” specify the presence of statedfeatures but do not preclude the presence or addition of one or moreother features. It will be further understood that when a particularstep of a method is referred to as subsequent to another step, it candirectly follow said other step or one or more intermediate steps may becarried out before carrying out the particular step, unless specifiedotherwise. Likewise it will be understood that when a connection betweenstructures or components is described, this connection may beestablished directly or through intermediate structures or componentsunless specified otherwise.

The description of the exemplary embodiments is intended to be read inconnection with the accompanying drawings, which are to be consideredpart of the entire written description. In the drawings, the absoluteand relative sizes of systems, components, layers, and regions may beexaggerated for clarity. Embodiments may be described with reference toschematic and/or cross-section illustrations of possibly idealizedembodiments and intermediate structures of the invention. In thedescription and drawings, like numbers refer to like elementsthroughout. Relative terms as well as derivatives thereof should beconstrued to refer to the orientation as then described or as shown inthe drawing under discussion. These relative terms are for convenienceof description and do not require that the system be constructed oroperated in a particular orientation unless stated otherwise.

FIGS. 1A and 1B schematically illustrate an embodiment for transfer andsoldering of a chip 1 a to a substrate 3.

According to one aspect, the figure illustrates a method for soldering achip 1 a to a substrate 3. A chip carrier 8 is provided between a flashlamp 5 and a substrate 3. A chip 1 a is attached to the chip carrier 8on a side of the chip carrier 8 facing the substrate 3. A soldermaterial 2 is disposed between the chip 1 a and the substrate 3. Theflash lamp 5 generates a light pulse 6 for heating the chip 1 a. Theheating of the chip 1 a causes the chip 1 a to be released from the chipcarrier 8 towards the substrate 3. The solder material 2 is at leastpartially melted by contact with the heated chip 1 a for attaching thechip 1 a to the substrate 3.

According to another or further aspect, the figure also illustratesparts of an apparatus for soldering a chip 1 a to a substrate 3. Forexample, the apparatus comprises a substrate handler 4 configured todetermine a location of the substrate 3. In the shown embodiment, thesubstrate handler 4 comprises rollers to handle e.g. a flexiblesubstrate in a roll-to-roll process. Also types of substrate handlersare possible, e.g. a platform to hold a separate sheet or board of asubstrate. Furthermore, the apparatus may comprise a carrier handler 18configured to determine a location of a chip carrier 8 with the chip 1 aattached on a side of the chip carrier 8 facing the substrate 3. In theshown embodiment, the carrier handler 18 comprises rollers, e.g. tohandle a carrier substrate 8 in a roll-to-roll process. The apparatuspreferably comprises an alignment device and controller (not shown).These may be configured to align the chip 1 a attached to the chipcarrier 8 with respect to a destination position 3 t of the chip 1 a onthe substrate 3, e.g. electrical conducting tracks on the substratesurface. For example, the carrier substrate 8 and destination substrate3 are aligned to moved synchronously wherein the chip 1 a is held abovethe tracks 3 t.

In one embodiment, the chip carrier 8 comprises a carrier substrate thatis transparent to the light pulse 6, wherein the chip 1 a is heated bythe light pulse 6 transmitted through the chip carrier 8. In a furtherembodiment, the chip carrier 8 comprises a transparent polymer film or atransparent glass substrate with a sacrificial adhesion layer. Forexample, the chip carrier 8 comprises so-called “standardized (blue)transparent polymer film” on which the silicon wafer is typicallyplaced. This means that in principle the manufacturer of these cutwafers does not have to change their processing. Also other chip carriersubstrates can be used, e.g. so-called “purple adhesive tape”.Preferably thin (e.g. silicon) chips of less than 50 microns thick areused to facilitate heat transport from the top to the base in order tosolder.

In one embodiment, the light 6 a of the light pulse 6 causesdecomposition of an adhesive material 8 a between the chip carrier 8 andthe chip 1 a thereby releasing the chip 1 a from the chip carrier 8. Theadhesive material may be part of the chip carrier 8 or a separateadhesive layer is formed between the chip and carrier. In oneembodiment, the chip 1 a is at least partially transferred by and/oralong a gravitational direction towards the substrate 3. Alternatively,or in addition, the release from the chip carrier 8 may cause the chip 1a to have an initial velocity towards the substrate 3. For example,decomposition of adhesive material 8 a causes gas formation thatlaunches the chip 1 a towards the substrate 3. For example, the rapidgas formation may provide the chip 1 a with an initial impulse.

In one embodiment, the chip 1 a is attached to the chip carrier 8 at adistance Z of at least 50 micrometer, preferably at least 100 micrometerfrom the substrate 3. At closer distances, the chips may startaccidentally contacting the substrate 3 before being transferred. Inanother or further embodiment, the chip 1 a is at a distance Z of atmost one millimeter, preferably at most 500 micrometer from thesubstrate 3. At larger distances, control over the positioning of thechip may deteriorate. For example, a gap between the chip and thedestination substrate (including any conducting tracks and/or solderbumps) is at 125 micrometer. This may provide alignment accuracy ofabout 10 microns. For example, the substrate 3 comprises a polyimidewith twelve micron thick copper tracks and solder bumps. Also otherdistances are possible, depending on the desired amount of control overthe positioning of the chip. The distance Z can be measured between thefacing surfaces of the substrates 3 and 8 or, alternatively, between thefacing surface of the (thickest) chip and the contact points on thesubstrate 3, including any solder material there between. In the lattercase the distance Z is a measure of the distance that the chip cantravel between the carrier and the destination substrate.

In one embodiment, the transmitted light 6 a of the light pulse 6continues to irradiate the chip 1 a while it is in transit (not shown)over a distance Z between the chip carrier 8 and the substrate 3. Inanother or further embodiment, the transmitted light 6 a of the lightpulse 6 continues to irradiate the chip 1 a while it is positioned onthe substrate 3 (FIG. 1B). In another or further embodiment, anintensity Ia of the light impinging the chip 1 a is modulated as afunction of time. For example, the light intensity Ia is higher at amoment when the chip is released from the chip carrier 8 than during atime of transit of the chip 1 a between the chip carrier 8 and thesubstrate 3, and wherein the light intensity Ia is increased after thetransit when the chip contacts the solder material 2 on the substrate 3.In another or further embodiment, the light intensity of the light 6 ais higher at a moment when the chip is released from the chip carrier 8than during a time of transit of the chip 1 a between the chip carrier 8and the substrate 3. In another or further embodiment, the lightintensity of the light 6 a is higher at a moment when the chip contactsthe solder material 2 than during a time of transit of the chip 1 abetween the chip carrier 8 and the substrate 3. In another or furtherembodiment, the light intensity of the light 6 a is higher at a momentwhen the chip is released from the chip carrier 8 than at a moment whenthe chip contacts the solder material 2 on the substrate 3. For example,light modulation is caused by the flash lamp 5 and/or a masking devicebetween the flash lamp and substrate

Preferably, a millisecond light pulse 6 is used e.g. produced by a(pulsed) Xenon flash lamp. A typical pulse may deliver a total energybetween 1 and 20 J/cm² e.g. in a pulse time between 0.5 to 10 ms. Forexample, a Xenon or other high intensity flash lamp can be used, e.g.with a pulse length of 2 ms and pulse intensity of 10 J/cm². A flashlamp, also called flashtube, typically comprises an electric arc lampconfigured to produce intense (incoherent) light for short durations,e.g. light pulses having a pulse length between 500 microseconds and 20milliseconds. Also shorter or longer pulses may be possible. Flashtubesare for example made of a length of glass tubing with electrodes ateither end and are filled with a gas that, when triggered, ionizes andconducts a high voltage pulse to produce the light. For example a Xenonflash lamp can be used to produce high light intensities sufficient toirradiate a chip surface and at least partially melt a solder materialin contact with the chip e.g. by heat conducted through the chip.

FIGS. 2A and 2B schematically illustrate a further embodiment, wherein amasking device 7 is disposed between the flash lamp 5 and the chip 1 a.The masking device 7 may at least partially block part of the lightpulse 6 from directly irradiating the substrate 3 and/or chip carrier 8around the chip. In one embodiment, the masking device 7 comprises amasking pattern 7 a,7 c disposed between the flash lamp 5 and the chip 1a. For example, the masking pattern 7 a,7 c is configured to selectivelypass light 6 a of the light pulse 6 to the chip 1 a and block otherlight not impinging the chip 1 a from reaching the substrate 3. Forexample, in one embodiment, a high intensity pulsed xenon flash lamp isused in combination with a (lithographical) mask to pattern the lightpulse impinging the chips. In another or further embodiment, the chipcarrier 8 and/or masking device 7 are comprised in a flexible foil, e.g.having variable transmission for different areas where chips areattached.

FIG. 3A schematically illustrates an embodiment, wherein the maskingdevice 7 is integrated as a layer on top of the chip carrier substrate8.

FIG. 3B shows another embodiment with even further integration of themasking device 7 and chip carrier 8 in a single substrate. In oneembodiment, the masking device 7 comprises a foil with varying degreesof transparency depending on where chips are attached. For example, thearea 7 a may transparent for providing the full intensity of the pulseto a first chip 7 a, and another area (not shown) may be partiallyopaque or semi-transparent for attenuating light of the pulse 6 e.g.impinging a second chip, e.g. having a lower heat capacity perilluminated area.

FIGS. 4A and 4B schematically show an embodiment wherein a plurality ofchips 1 a, 1 b are simultaneously transferred from the chip carrier 8 tothe substrate 3 and soldered to the substrate 3. Advantageously, thetransfer and soldering of one or more chips can be effected by a singlelight pulse 6.

In one embodiment, two or more different chips 1 a, 1 b having differentheating properties C1,C2 are attached to the chip carrier 8. In anotheror further embodiment, a masking device 7 is disposed between the flashlamp 5 and the chips 1 a, 1 b causing different light intensities Ia,Ibin different areas 6 a,6 b of the light pulse 6 passing the maskingdevice 7. Accordingly, the chips 1 a, 1 b can be heated with differentlight intensities Ia,Ib for at least partially compensating thedifferent heating properties C1,C2 to reduce a spread in temperaturebetween the chips as a result of the heating by the light pulse 6.

In one embodiment, the apparatus comprises a substrate handler 4configured to determine a location of the substrate 3 and/or chips 1 a,1 b. For example, the apparatus comprises a sensor (not shown)configured to determine a location of the chips 1 a, 1 b with respect tothe substrate 3.

In one embodiment, the light pulse 6 is simultaneously transmitted tothe chips 1 a, 1 b via a mask pattern 7 a,7 b,7 c of the masking device7. For example, the mask pattern 7 a,7 b,7 c comprises a first filterregion 7 a passing a first part 6 a of the light pulse 6 with a firstlight intensity Ia to a first chip 1 a; and a second filter region 7 bpassing a second part 6 b of the light pulse 6 with a second lightintensity Ib to a second chip 1 b, wherein the first light intensity Iais different than the second light intensity Ib. Light intensity ismeasured e.g. per unit area of the chip surface receiving the part ofthe light pulse.

In one embodiment, the first chip 1 a has a first heat capacity C1 andthe second chip 1 b has a second heat capacity C2 different from thefirst heat capacity C1. For example in the shown embodiment, the firstchip 1 a is thinner than the second chip 1 b. An object's heat capacityis defined e.g. as the ratio of the amount of heat energy transferred toan object and the resulting increase in temperature of the object. Heatcapacity may be larger for larger objects or for objects containing amaterial with larger specific heat capacity (per unit mass) orvolumetric heat capacity (per unit volume). Preferably, the differentlight intensities Ia,Ib at least partially compensate a difference inheat capacity C1,C2 or other difference in heating property between thedifferent chips 1 a, 1 b for reducing a spread in temperature of thechips heated by the light pulse 6.

In one example, two components having different thicknesses and surfaceareas may need a different input energy for soldering components. Forexample, a lower thickness and surface may result in a low heat capacityleading to a relatively high temperature increase per input energy unit,while on the contrary a reduced number of solder bonds may require lowerinput energy for soldering corresponding bonds. Using a mask withcorresponding transmittance filters, exposure fluence can be locallytuned allowing for different chips to be soldered with a single pulse.Filters could be for example either with fixed or configurabletransmittance.

In one embodiment, the apparatus comprises optional illumination optics(not shown) configured to homogeneously illuminate an area of themasking device 7 with the mask pattern 7 a,7 b,7 c. In another orfurther embodiment, the apparatus comprises optional projection optics(not shown) configured to project an image of the mask pattern 7 a,7 b,7c onto the chips 1 a, 1 b. In the embodiment shown, the transmittedlight 6 a,6 b of the light pulse 6 is projected onto the chips 1 a, 1 bwhile they are positioned on the substrate 3 with the solder material 2there between thereby heating the chips 1 a, 1 b. The heated chips 1 a,1 b may cause the at least partial melting of the solder material 2 forattaching the chips 1 a, 1 b to the substrate 3 (afterresolidification).

In one embodiment, the masking device 7 comprises a mask pattern 7 a,7b,7 c configured to selectively transmit the light pulse 6 to the chips1 a, 1 b. In another or further embodiment, the mask pattern 7 a,7 b,7 ccomprises a first filter region 7 a having a first transmissioncoefficient Ta configured to transmit light 6 a of the light pulse 6with a first light intensity Ia to a first chip 1 a for melting a soldermaterial 2 between the first chip 1 a and the substrate 3; and a secondfilter region 7 b having a second transmission coefficient Tb configuredto transmit light 6 b of the light pulse 6 with a second light intensityIb to a second chip 1 b for melting a solder material 2 between thesecond chip 1 a and the substrate 3. In a further embodiment, the firsttransmission coefficient Ta is different than the second transmissioncoefficient Tb for simultaneously irradiating the chips 1 a, 1 b withdifferent light intensities Ib,Ib. The transmission coefficient is ameasure of how much of an electromagnetic wave (light) passes a surfaceor an optical element. For example, transmission coefficients can becalculated for either the amplitude or the intensity of the wave. Eitheris calculated by taking the ratio of the value after the surface orelement to the value before.

In one embodiment, the filter regions 7 a,7 b,7 c of the mask patternare controllable to tune the transmission coefficients Ta,Tb. Forexample, the mask pattern 7 a,7 b,7 c is formed by tunable optics, e.g.a grid of digital mirrors, LCD, and/or polarizing optics. In oneembodiment, the mask pattern 7 a,7 b,7 c comprises a third filter region7 c having a third transmission coefficient Tc configured tosubstantially block part of the light pulse 6, e.g. a part that wouldotherwise be directly projected onto the substrate 3.

In one embodiment, the masking device 7 comprises photolithographedmetal on glass. For example, aluminium or chrome is used to vary thelight intensity of the pulse in two, three, or more differentintensities. In one embodiment, the masking device 7 comprises a coolingdevice (not shown), e.g. water cooling to handle (partial) absorption ofhigh energy light pulses.

FIG. 5A shows an apparatus for soldering a chip 1 a onto a substrate 3,wherein the masking device 7 comprises a first filter region 7 a withpixels 7 p having a first transmission coefficient Ta to transmit light6 a of the light pulse 6 with the first light intensity Ia to the firstchip 1 a.

FIG. 5B shows an apparatus for soldering a chip 1 a onto a substrate 3,wherein a filter region 7 a transmitting part 6 a of the light pulse 6to a chip 1 a comprises multiple pixels 7 p having differenttransmission coefficients, wherein the first light intensity Ia isdetermined by a combination light intensities transmitted by the pixels7 p having different transmission coefficients. For example, a ditheredpattern of pixels can be used to reduce the overall or average intensityIa of light 6 a impinging the chip 1 a. The embodiments of FIGS. 5A and5B can e.g. be used in combination with a chip carrier between themasking device 7 and substrate 3.

FIG. 6A illustrates an embodiment of an apparatus for transfer andsoldering of chips in a roll-to-roll fabrication process. In the shownembodiment, the substrate handler 4 comprises rolls to handle the foilsubstrate 3 which may be flexible. In another or further embodiment, thechip carrier 8 and/or masking device 7 are also comprised in a flexiblefoil. In another or further embodiment, the chip carrier 8 and/ormasking device 7 are configured to move in synchronicity with thesubstrate 3. In one embodiment, the flash lamp 5 is configured todeliver a single pulse 6 to transfer and solder multiple chips 1 a, 1 bhaving possibly different sizes or other heating properties.

In the embodiment the apparatus comprises an alignment device 12 (e.g.camera or other sensor) and a controller 15. In another or furtherembodiment, the apparatus comprises a controller 15 configured tocontrol the alignment device 12, substrate handler 4 and/or substratehandler 4. For example, the controller 15 is programmed to align thechips attached to the chip carrier 8 with respect to destinationpositions on the substrate 3. Alternatively, or in addition, thecontroller 15 is programmed to align the different light intensities ofthe different areas 6 a,6 b of the light pulse 6 with locations of thedifferent chips 1 a, 1 b.

FIG. 6B illustrates another embodiment of an apparatus for soldering ofchips in a roll-to-roll fabrication process. In the embodiment, avariably tuned masking device 7 is used at a fixed position e.g. above achip carrier 8 held by a suitable carrier handler (not shown)

In one embodiment, the apparatus comprises a controller 15 configured tovariably tune the light intensities Ia,Ib in dependence of therespective sizes of the chips 1 a, 1 b. In one embodiment, a controller15 is configured to determine locations of the chips 1 a, 1 b from achip location device and to control the masking device 7 and/orsubstrate handler 4. For example, the controller 15 is programmed toalign the different light intensities of the different areas 6 a,6 b ofthe light pulse 6 with locations of the different chips 1 a, 1 b. Forexample, the controller 15 is programmed to control the transmissioncoefficients of the filter regions of the masking device 7 in dependenceof the respective sizes of the chips 1 a, 1 b.

In one embodiment, the controller 15 is programmed to set a relativelyhigh light intensity for a part 6 b of the light pulse 6 intended for achip 1 b having a relatively high heat capacity per illuminated area,e.g. a relatively thick chip. In another or further embodiment, thecontroller 15 is programmed to set a relatively low light intensity fora part 6 a of the light pulse 6 intended for a chip 1 a having arelatively low heat capacity per illuminated area, e.g. a relativelythin chip. In one embodiment, the controller 15 is programmed to set arelatively higher transmission coefficient Tb for a part 6 b of thelight pulse 6 intended for a relatively larger size chip 1 b and arelatively lower transmission coefficient Ta for a part 6 a of the lightpulse 6 intended for a relatively smaller size chip 1 a.

In one embodiment, the apparatus comprises a sensor 12 (e.g. camera)configured to detect a location the tracks 13 on the substrate 3. Thesensor 12 may provide feedback to the controller 15 which can be used toalign the position of the chips and/or intensity of the light. In oneembodiment, the substrate handler 4 is configured to slow down or stopmovement of the substrate 3 while the light 6 a,6 b is applied to thechips 1 a, 1 b.

In one embodiment, the apparatus comprises a solder supply unit 9configured to apply the solder material 2 to the substrate 3 and/orchips 1 a, 1 b before the chips 1 a, 1 b are placed on the substrate 3with the solder material 2 there between. For example, the solder supplyunit 9 comprises a blade coating device and/or a stencilling device.

In one embodiment, the apparatus comprises a track application unit 10configured to apply, e.g. print, conductive tracks to the substrate 3before the solder material 2 is applied, wherein, in use, the chips 1 a,1 b are electrically connected to the tracks.

For the purpose of clarity and a concise description, features aredescribed herein as part of the same or separate embodiments, however,it will be appreciated that the scope of the invention may includeembodiments having combinations of all or some of the featuresdescribed. For example, it will be clear that the devices described withreference to FIGS. 6A and 6B can also be used in other embodiments thanroll-to-roll processing. For example, the controller 15 can also be usedto control placement of chips on a fixed substrate Also the otherdevices 10, 9, 12 as described herein can be applied in otherembodiments, alone or in any combination, possibly under separate orshared control of a controller 15 as described herein. The controllermay be programmed with software that allow it to execute operationalsteps in accordance with methods as described herein with reference toany of the embodiments.

Also other combinations will be readily apparent to the skilled artisanhaving the benefit of the present disclosure for achieving a similarfunction and result. For example electronic and mechanical componentsmay be combined or split up into one or more alternative components. Thevarious elements of the embodiments as discussed and shown offer certainadvantages, such as fast and reliable soldering of chips and/orcontactless transfer of chip. Of course, it is to be appreciated thatany one of the above embodiments or processes may be combined with oneor more other embodiments or processes to provide even furtherimprovements in finding and matching designs and advantages. It isappreciated that this disclosure offers particular advantages toroll-to-roll processing, and in general can be applied for anyapplication wherein chips are soldered.

Finally, the above-discussion is intended to be merely illustrative ofthe present systems and/or methods and should not be construed aslimiting the appended claims to any particular embodiment or group ofembodiments. The specification and drawings are accordingly to beregarded in an illustrative manner and are not intended to limit thescope of the appended claims. In interpreting the appended claims, itshould be understood that the word “comprising” does not exclude thepresence of other elements or acts than those listed in a given claim;the word “a” or “an” preceding an element does not exclude the presenceof a plurality of such elements; any reference signs in the claims donot limit their scope; several “means” may be represented by the same ordifferent item(s) or implemented structure or function; any of thedisclosed devices or portions thereof may be combined together orseparated into further portions unless specifically stated otherwise.The mere fact that certain measures are recited in mutually differentclaims does not indicate that a combination of these measures cannot beused to advantage. In particular, all working combinations of the claimsare considered inherently disclosed.

The invention claimed is:
 1. A method for soldering a chip to asubstrate, the method comprising: providing a chip carrier between aflash lamp and the substrate, wherein the chip is attached to the chipcarrier on a side of the chip carrier facing the substrate, and whereina solder material is disposed between the chip and the substrate; andgenerating a light pulse with the flash lamp for heating the chip,wherein the light pulse heating of the chip causes the chip to bereleased from the chip carrier to transfer contactlessly towards thesubstrate, and wherein the solder material is melted by contact with thechip, after the chip is heated by the light pulse, for attaching thechip to the substrate.
 2. The method according to claim 1, wherein atransmitted light of the light pulse from the flash lamp continues toirradiate the chip while the chip is contactlessly in transit over adistance between the chip carrier and the substrate.
 3. The methodaccording to claim 2, wherein an intensity of the transmitted lightimpinging the chip is modulated as a function of time by at least one ofthe group consisting of: a controlling of the light pulse of the flashlamp, and a masking device between the flash lamp and chip carrier,wherein, by said modulation, an intensity of the transmitted light ishigher at a moment when the chip is released from the chip carrier thanduring a time of transit of the chip between the chip carrier and thesubstrate.
 4. The method according to claim 3, wherein the transmittedlight of the light pulse continues to irradiate the chip while it ispositioned on the substrate, and wherein an intensity of the transmittedlight is increased after the transit when the chip contacts the soldermaterial on the substrate.
 5. The method according to claim 1, whereinthe chip carrier comprises a carrier substrate that is transparent tothe light pulse, and wherein the chip is heated by the light pulse thatis transmitted through carrier substrate of the chip carrier.
 6. Themethod according to claim 1, wherein the light of the light pulse causesdecomposition of an adhesive material between the chip carrier and thechip thereby releasing the chip from the chip carrier.
 7. The methodaccording to claim 1, wherein the chip is attached to the chip carrierat a distance from the substrate, and wherein the distance is between 50and 500 micrometer.
 8. The method according to claim 1, wherein amasking device comprises a masking pattern, wherein the masking deviceis disposed between the flash lamp and the chip, and wherein the maskingpattern is configured to selectively pass light of the light pulse tothe chip.
 9. The method according to claim 1, wherein a plurality ofchips are simultaneously transferred from the chip carrier to thesubstrate and soldered to the substrate.
 10. The method according toclaim 1, wherein the transfer and soldering of one or more chips iseffected by a single light pulse.
 11. The method according to claim 1,wherein two or more different chips having different heating propertiesare attached to the chip carrier; and a masking device is disposedbetween the flash lamp and the two or more different chips to causedifferent light intensities in different areas of the light pulsepassing the masking device, and thereby heating individual ones of thetwo or more different chips with different light intensities, andwherein the different light intensities at least partially compensatethe different heating properties to reduce a spread in temperature ofthe two or more different chips as a result of heating by the lightpulses from the flash lamp.
 12. The method according to claim 1, whereinthe substrate comprises a flexible foil in a roll-to-roll process.